Sheet discharging device

ABSTRACT

A sheet discharging device includes a sheet discharging section which discharges sheets, and a sheet discharging tray including a stacking wall portion on which discharged sheets are stacked. The stacking wall portion includes a first wall portion having a first surface which becomes higher in a direction in which sheets are discharged, and a second wall portion connected to an upstream end of the first wall portion in the sheet discharging direction and having a second surface including at least one of a horizontal surface, an inclined surface having a smaller gradient than that of the first surface, and an inclined surface having a gradient opposite to that of the first surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-201875, filed Jul. 11, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet discharging device mounted in,for example, an auto document feeder in an image forming apparatus todischarge loaded sheets to a sheet discharging tray or the like.

2. Description of the Related Art

Some image forming apparatuses such as copiers are provided with an autodocument feeder (ADF). The auto document feeder takes out each of thedocuments (sheets) stacked in a sheet feeding tray and feeds it to aread position in the image forming apparatus. Then, after an image isread, the auto document feeder discharges the sheet to a sheetdischarging tray. The auto document feeder is thus provided with a sheetfeeding device consisting of a sheet discharging portion that dischargesdocuments from which images have been read and a sheet discharging traythat accommodates the discharged documents.

One problem with the conventional sheet discharging device is that avariation in document discharging speed, document size, or the likesuppresses the alignment of documents on the sheet discharging tray,that is, the alignment of discharged sheets. The main cause of thesuppressed alignment of discharged sheets is that the leading end of adischarged document hangs down owing to gravity and comes into contactwith the surface of the documents already discharged onto the sheetdischarging tray, thus moving the documents on the sheet dischargingtray.

To solve this problem, a technique has been developed which corrugatesdocuments to be discharged to allow them to advance straight moreproperly when discharged. When a discharged document advances straightmore properly, its leading end comes into contact with documents on thesheet discharging tray at a position farther than the one achievedwithout using this technique. This reduces the time for which and thearea over which the discharged document contacts the surface of thedocuments on the sheet discharging tray. The alignment of dischargeddocuments is thus improved.

Another technique has been developed which uses an inclined sheetdischarging tray to slide down discharged documents backward to aligntheir trailing ends together at a rear end wall of the sheet dischargingtray. However, the inclined sheet discharging tray requires an increasein the vertical size of the sheet discharging tray and thus in the sizeof the device. A technique has thus been developed which forms the rearend of the sheet discharging tray into a gently inclined or flat surfaceto avoid an increase in the height of the sheet discharging tray.

A technique has also been developed which provides the sheet dischargingtray with a leading end wall to align the leading ends of dischargeddocuments together at the leading end wall instead of aligning theirtrailing ends at the trailing end wall of the sheet discharging tray.

Another technique has been developed which makes the inclination of rearof the sheet display tray smaller to avoid an increase in the verticalsize of the sheet discharging tray, while providing the sheetdischarging tray with a leading end wall to align the leading ends ofdischarged documents together at the leading end wall. This leading endwall is movable with respect to the sheet discharging tray to adjust todocuments of multiple sizes (see, for example, Jpn. Pat. Appln. KOKAIPublication No. 7-277579).

A considerably marked corrugation is required to prevent the leading endof a document from coming into contact with the documents on the sheetdischarging tray until the document is completely discharged. However, amarked corrugation significantly stresses the document, which may thusbe damaged.

Jpn. Pat. Appln. KOKAI Publication No. 7-277579 reliably reduces thesize of the device. However, the movability of the leading end wallprevents the alignment of discharged documents from being improvedunless the position of the leading end wall adjusts to the documentsize.

For example, if the leading end wall lies distally with respect to thedocument size, the leading end of a discharged document cannot reach theleading end wall. The discharged document thus fails to be aligned withthe documents on the sheet discharging tray. On the contrary, if theleading end wall lies proximally with respect to the document size, theleading end of the document collides against the leading end wall beforethe document is completely discharged. The document may thus be bent.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a sheet discharging device that canreliably improve the alignment of discharged sheets on a sheetdischarging tray without imposing a heavy load on the sheets and withoutthe need to increase the size of the entire device.

An aspect of the present invention configures a sheet discharging deviceas described below.

The sheet discharging device comprises a sheet discharging portion whichdischarges sheets, and a sheet discharging tray including a stackingwall portion on which discharged sheets are stacked. The stacking wallportion comprises a first wall portion having a first surface whichbecomes higher in a direction in which sheets are discharged, and asecond wall portion connected to an upstream end of the first wallportion in the sheet discharging direction and having a second surfaceincluding at least one of a horizontal surface, an inclined surfacehaving a smaller gradient than that of the first surface, and aninclined surface having a gradient opposite to that of the firstsurface.

Another aspect of the present invention configures a sheet dischargingdevice as described below.

The sheet discharging device comprises a sheet discharging portion whichdischarges sheets, and a sheet discharging tray including a stackingwall portion on which discharged sheets are stacked. The sheetdischarging tray comprises a projecting portion having a wall portionprovided in a central portion of the sheet discharging tray in a widthdirection substantially orthogonal to the sheet discharging direction toraise a width-wise central portion of the sheets stacked on the sheetdischarging tray. The wall portion comprises a first wall portion havinga first surface which becomes higher in a direction in which sheets aredischarged, and a second wall portion connected to an upstream end ofthe first wall portion in the sheet discharging direction and having asecond surface including at least one of a horizontal surface, aninclined surface having a smaller gradient than that of the firstsurface, and an inclined surface having a gradient opposite to that ofthe first surface.

The present invention reliably improves the alignment of dischargeddocuments on the sheet discharging tray without imposing a heavy load onthe sheets and without the need to increase the size of the device.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a front view showing a digital copier in accordance with anembodiment of the present invention;

FIG. 2 is a perspective view showing an auto document feeder inaccordance with the embodiment;

FIG. 3 is a perspective view showing an auto document feeder from whicha sheet feeding tray has been removed in accordance with the embodiment;

FIG. 4 is a sectional view showing the internal configuration of theauto document feeder in accordance with the embodiment;

FIG. 5 is a schematic diagram showing a sheet discharging device inaccordance with the embodiment as viewed from a downstream side in adirection in which documents are conveyed;

FIG. 6 is an enlarged sectional view showing a sheet discharging tray inaccordance with the embodiment; and

FIG. 7 is an enlarged sectional view showing a variation of the sheetdischarging tray in accordance with the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below in detailwith reference to the drawings.

(Configuration of a Digital Copier)

FIG. 1 is a diagram showing the appearance of a digital copier inaccordance with an embodiment of the present invention. As shown in FIG.1, the digital copier comprises an auto document feeder (ADF) 10, ascanner unit 20, and a printer engine section 30.

With the digital copier, the maximum copy document size is called a fullsize. Half the maximum copy document size is called a half size.Accordingly, in the present embodiment, in which the maximum copydocument size is A3, the A3 size corresponds to the full size and an A4size, which is half the A3 size, corresponds to the half size.

The auto document feeder 10 loads and supplies each document (sheet) Dto a predetermined read position R (described later).

The scanner unit 20 optically reads an image from the document Dsupplied by the auto document feeder 10 or manually to convert the imageinto image data.

The printer engine section 30 comprises a charger, a laser unit, aphotosensitive drum, a developing device, a transfer roller, and afixing device (none of them are shown). The charger charges a surface ofthe photosensitive drum to a predetermined potential. The laser unitforms an electrostatic latent image on the surface of the photosensitivedrum on the basis of image data from the scanner unit 20. The developingdevice develops the electrostatic latent image on the photosensitivedrum using toner. The transfer roller transfers the toner image formedon the photosensitive drum to a sheet. The fixing device fixes the tonerimage transferred to the sheet. In this configuration, the printerengine section 30 copies the document image read by the scanner unit 20to the sheet.

(Configuration of the Auto Document Feeder 10)

FIG. 2 is a perspective view showing the auto document feeder 10 inaccordance with the embodiment of the present invention. FIG. 3 is aperspective view showing the auto document feeder 10 from which thesheet feeding tray 11 has been removed in accordance with theembodiment. FIG. 4 is a sectional view showing the internalconfiguration of the auto document feeder 10 in accordance with theembodiment.

As shown in FIGS. 2 to 4, the auto document feeder 10 is composed of asheet feeding tray 11 on which a plurality of documents D are placed, aconveying device 12 that takes each of the documents D out of the sheetfeeding tray 11 to convey the document D along a conveying path C(described later), and a sheet discharging tray 13 that accommodates aplurality of documents D discharged by the conveying device 12.

The conveying device 12 comprises a first and second guide members 121and 122. The first and second guide members 121 and 122 compriserespective smooth guide surfaces inside. The U-shaped conveying path Cis provided in the gap between the guide surfaces so that the document Dcan be conveyed along the conveying path C.

The conveying path C connects the sheet feeding tray 11 and the sheetdischarging tray 13 together. The read position R is provided in aportion of the conveying path C which is closest to the scanner unit 20;a document image is read at the read position R.

The first guide member 121 is placed outside the second guide member122. The first guide member 121 has a rectangular opening 121 a formedin its area corresponding to the read position R. This allows thedocument D conveyed along the conveying path C to be located oppositethe scanner unit 20 on passing through the read position R.

The conveying path C has a pickup roller 123, a separate roller 124, aregistration roller 125, a first conveying roller 126 a, a secondconveying roller 126 b, a stabilizing roller 127, a third conveyingroller 126 c, and a sheet discharging roller 128 which are arranged inthis order from an upstream side in a direction in which the document Dis conveyed.

The pickup roller 123 picks up each of the documents D in the sheetfeeding tray 11 and loads it into the conveying path C of the conveyingdevice 12. When a plurality of documents D are loaded by the pickuproller 123, the separate roller 124 passes only the uppermost document Dthrough, while blocking the passage of the remaining documents D. Theregistration roller 125 registers the document D the passage of which isnot blocked by the separate roller 124. The first to third conveyingrollers 126 a to 126 c convey the document D registered by theregistration roller 125, along the conveying path C. The stabilizingroller 127 stabilizes the behavior of the document D conveyed by thefirst to third conveying rollers 126 a to 126 c. The sheet dischargingroller 128 constitutes a sheet discharging device 40 together with thesheet discharging tray 13. The sheet discharging roller 128 dischargesthe document D conveyed by the first to third conveying rollers 126 a to126 c, from the conveying path C.

Each of the rollers 123 to 128 has a plurality of (in the presentembodiment, four) roller pieces around a horizontally supported driveshaft at predetermined intervals. When each of the drive shafts isrotated, all roller pieces provided around the drive shaft rotateconcurrently.

Pinch rollers 129 are arranged immediately below the respective sheetdischarging roller pieces 128. Each of the pinch rollers 129 isrotatably disposed in a groove portion 121 b (shown only in FIG. 5) ofthe first guide member 121. Each of the pinch rollers 129 is contactedwith an outer peripheral surface of the sheet discharging roller 128under pressure by elastic means such as a leaf spring.

The separate roller 124, registration roller 125, first to thirdconveying roller 126 a to 126 c, and sheet discharging roller 128constitute respective roller pairs together with driven rollers arrangedopposite them across the conveying path C. For example, the separateroller 124 constitutes a separate roller pair together with acorresponding driven roller.

That portion of the first guide member 121 which lies downstream of theread position R is located below that portion of the second guide member122 which lies downstream of the read position R. Thus, in thedescription below, the portion of the first guide member 121 locateddownstream of the read position R is called a lower guide portion 121 c.The portion of the second guide member 122 located downstream of theread position R is called an upper guide portion 122 c.

FIG. 5 is a schematic diagram showing the sheet discharging device 40 inaccordance with the embodiment as viewed from a downstream side in thedirection in which the document D is conveyed. As shown in FIG. 5, thelower guide portion (guide member) 121 c has a guide surface locatedbelow the lowermost portion of the sheet discharging roller 128. Thelower guide portion 121 c comprises a plurality of (in the presentembodiment, four) projecting portions 130 located substantiallyimmediately below the drive shaft of the sheet discharging roller 128.The number of projecting portions 130 is not particularly limited.

The projecting portions 130 are disposed so that two of the four sheetdischarging roller pieces 128 arranged at the opposite ends of the sheetdischarging roller are each sandwiched between the projecting portions130. The upper end of each projecting portion 130 projects upward fromthe lowermost portion of the sheet discharging roller 128.

Each projecting portion 130 comprises a scoop-up surface in its arealocated upstream in the conveying direction of the document D; thescoop-up surface becomes higher as it approaches its downstream end inthe conveying direction. Thus, when the document D reaches theprojecting portions 130, a portion of the document D which correspondsto the projecting portions 130 is scooped up by the scoop-up surface andruns onto the projecting portions 130. On the other hand, a portion ofthe document D which corresponds to the sheet discharging roller 128 isguided by the upper and lower guide portions 121 c and 122 c as it isand then advances between the sheet discharging roller 128 and the pinchroller 129.

(Configuration of the Sheet Discharging Tray 13)

Now, the sheet discharging tray 13 will be described with reference toFIG. 6.

FIG. 6 is a sectional view showing the sheet discharging tray 13 inaccordance with the embodiment. In the description below, a sheetdischarging direction refers to the direction in which the document D isdischarged. A width direction refers to the direction orthogonal to thesheet discharging direction in a horizontal plane.

As shown in FIG. 6, the sheet discharging tray 13 comprises a bottomwall portion (stacking wall portion) 131 on which the dischargeddocuments D are stacked, a rear wall portion 132 provided upstream ofthe bottom wall portion 131 in the sheet discharging direction to alignthe trailing ends of the documents D stacked on the bottom wall portion131, and side wall portions 133 provided at the opposite ends of thebottom wall portion 131 in the width direction to prevent the documentsD stacked on the bottom wall portion 131 from falling down.

The bottom wall portion 131 comprises a horizontal portion (fourth wallportion 131 a) and a ridge portion 131 b (shown only in FIG. 3); thehorizontal portion 131 a is closer to the rear wall portion 132 than theridge portion 131 b. A protruding portion 134 is provided in a centralportion of the bottom wall portion 131 in the width direction to raisethe width-wise central portion of the documents D stacked on the bottomwall portion 131.

The protruding portion 134 extends from a middle portion of thehorizontal portion 131 a to a rear end of the ridge portion 131 b. A topwall portion 140 is placed at a top portion of the protruding portion134. The upper wall portion 140 comprises a first inclined portion(third wall portion) 134 a, a second inclined portion (second wallportion) 134 b, a third inclined portion (first wall portion) 134 c, anda fourth inclined portion 134 d which are arranged in this order; thefirst inclined portion 134 a is closest to the rear wall portion 132,and the fourth inclined portion 134 d is farthest from the rear wallportion.

Each of the first to fourth inclined portions 134 a to 134 d is inclinedso as to become higher in the sheet discharging direction. The documentD placed on the sheet discharging tray 13 thus slides down toward therear wall portion 132.

The first inclined portion 134 a extends both upstream and downstream inthe sheet discharging direction by a predetermined length from aposition located at that distance from the rear wall portion 132 whichis almost equal to half of the vertical size of an A4-sized document D.In other words, the first inclined portion 134 a is formed within anarea including the position of the leading end of the A4-sized documentD with its trailing end abutting against the rear wall portion 132.

The third inclined portion 134 c extends both upstream and downstream inthe sheet discharging direction by a predetermined length from aposition located at that distance from the rear wall portion 132 whichis almost equal to the vertical size of the A4-sized document D.

Thus, when the A4-sized document is placed on the sheet discharging tray13, its middle portion corresponds to the first inclined portion 134 a,while its leading end corresponds to the third inclined portion 134 c.

If an A3-sized document is placed on the sheet discharging tray 13, twodifferent areas in the middle portion of the document D correspond tothe first and third inclined portions 134 a and 134 c.

The first inclined portion 134 a is steeper than the horizontal portion131 a, connected to an upstream end of the first inclined portion 134 ain the sheet discharging direction, and the second inclined portion 134b, connected to a downstream end of the first inclined portion 134 a inthe sheet discharging direction. The inclination of the first inclinedportion 134 a is utilized to prevent the documents D already stacked onthe sheet discharging tray 13 from moving in the sheet dischargingdirection.

The third inclined portion 134 c is steeper than the second inclinedportion 134 b, connected to an upstream end of the third inclinedportion 134 c in the sheet discharging direction, and the fourthinclined portion 134 d, connected to a downstream end of the thirdinclined portion 134 c in the sheet discharging direction. Theinclination of the third inclined portion 134 c is utilized to preventthe documents D already stacked on the sheet discharging tray 13 frommoving in the sheet discharging direction.

When the subsequently discharged document D exerts a frictional forceacting in the sheet discharging direction, on the documents D alreadystacked on the sheet discharging tray 13, the first and third inclinedportions 134 a and 134 c exert a resistance force on the documents D onthe sheet discharging tray 13 to offset the frictional force.

In particular, if the documents stacked on the sheet discharging trayare of the A4 size, their leading ends contact the first inclinedportion 134 a at a large friction angle. Accordingly, even if thesubsequently discharged document D exerts a strong frictional force inthe sheet discharging direction, a resistance force is exerted which issufficient to offset the frictional force.

Thus, even when the subsequently discharged document D applies africtional force acting in the sheet discharging direction, to thedocuments D stacked on the sheet discharging tray 13, the resistanceforce of the first and third inclined portions 134 a and 134 c preventsthe stacked documents D from moving in the sheet discharging direction.

The inclination of the third inclined portion 134 c is designed so thatwhile an A3-sized document D is being discharged by the sheetdischarging roller 128, the advancement of the document D is nothindered by the third inclined portion 134 c. Specifically, while theforce of the sheet discharging roller 128 is acting directly on theA3-sized document to push it out, the document D can slide on the thirdinclined portion 134 c. This enables the A3-sized document dischargedonto the sheet discharging tray 13 to advance smoothly to the fourthinclined portion 134 d without stopping at the third inclined portion134 c.

A sub sheet discharging tray 135 is housed in the leading end of thesheet discharging tray 13 so that it can project from and withdraw intothe sheet discharging tray 13. The sub sheet discharging tray 135 isdisposed at a distance from the rear wall portion 132 that is almostequal to the vertical size of the A3-sized document D. Thus, whenA3-sized documents D are stacked on the sheet discharging tray 13, theirleading end corresponds to the sub sheet discharging tray 135.

The sub sheet discharging tray 135 is steeper than the fourth inclinedportion 134 d. The sub sheet discharging tray 135 utilizes itsinclination to prevent A3-sized documents D stacked on the sheetdischarging tray 13 from moving in the sheet discharging direction.

When the subsequently discharged document D exerts a frictional force onthe A3-sized documents D already stacked on the sheet discharging tray13, the first and third inclined portions 134 a and 134 c and sub sheetdischarging tray 135 exert a resistance force on the A3-sized documentsD on the sheet discharging tray 13 to offset the frictional force.

Thus, even when the subsequently discharged document D applies africtional force acting in the sheet discharging direction, to theA3-sized documents D stacked on the sheet discharging tray 13, theresistance force of the first and third inclined portions 134 a and 134c and sub sheet discharging tray 135 prevents the stacked A3-sizeddocuments D from moving in the sheet discharging direction.

A plurality of ribs 136 (only shown in FIG. 3) are formed on the bottomwall portion 131, protruding portion 134, and sub sheet discharging tray135 of the sheet discharging tray 13 along the sheet dischargingdirection. These ribs 136 reduce the frictional force acting on themoving document D. The ribs 136 allow the documents D placed directly onthe bottom wall portion 131 of the sheet discharging tray 13 to slidedown smoothly toward the rear of the sheet discharging tray.

(Configuration of the Scanner Unit 20)

The scanner unit 20 comprises a glass plate (not shown) at a positioncorresponding to the read position R. The glass plate 21 is colorlessand transparent and has a reader (not shown) provided on its scannerunit 20 side. The reader comprises a first carriage, a second carriage,an image forming lens, and a CCD sensor (none of them are shown).

The first carriage is provided with an exposure lamp (not shown) thatirradiates the document D passing on a surface of the glass plate, and afirst mirror that reflects reflected light from the document surface ina predetermined direction. Second and third mirrors (not shown) areattached to the second carriage to reflect the reflected light from thefirst mirror in a predetermined direction.

The light emitted from the exposure lamp passes through the glass plateto the surface of the document D passing through the read position R.Then, the light reflected off the document surface passes through theglass plate back to the scanner unit 20. The light is reflected by thefirst to third mirrors and then guided to the image forming lens. Thelight converged by the image forming lens is detected by the CCD sensor.The detection signal is used to create image data.

A document glass board (not shown) is provided on the top surface of thescanner unit 20 so that the document D is manually placed on thedocument glass board. The document glass board is used to read adocument image without the use of the auto document feeder 10.

(Operation of Discharging the Document D)

The document D from which the document image has been read is conveyedto the sheet discharging roller 128 while being guided by the upper andlower guides 121 c and 122 c. Once the conveyed document D reaches theprojecting portions 130 of the lower guide portion 121 c, a portion ofthe document D which corresponds to the projecting portions 130 isscooped up by the scoop-up surface and runs onto the projecting portions130. However, a portion of the document D which corresponds to the sheetdischarging roller 128 is guided by the upper and lower guide portions121 c and 122 c as it is and then advances between the sheet dischargingroller 128 and the pinch roller 129.

This causes the different portions of the document D discharged onto thesheet discharging tray 130 to advance in the respective directions. As aresult, the document D discharged to the sheet discharging tray 13 has alocally substantially S-shaped cross section, that is, the document iscorrugated.

During the discharging process, the corrugated document D hangs downprogressively from its leading end and finally comes into contact withthe surface of the documents already stacked on the sheet dischargingtray 13. The discharged document D advances continuously in the sheetdischarging direction until its trailing end sandwiched between thesheet discharging roller 128 and the pinch roller 129 is released. Inthe meantime, a frictional force acting in the sheet dischargingdirection is continuously exerted on the documents D stacked on thesheet discharging tray 13.

However, if the documents stacked on the sheet discharging tray 13 areof the A4 size, their leading end corresponds to the third inclinedportion 134 c of the sheet discharging tray 13, while their middleportion corresponds to the first inclined portion 134 a. Consequently,even when a frictional force is exerted by the subsequently dischargeddocument D, the resistance force of the third inclined portions 134 aand 134 c prevents the documents D on the sheet discharging tray 13 frommoving in the sheet discharging direction.

Even when the documents stacked on the sheet discharging tray 13 are ofthe A3 size, their middle portion corresponds to the first and thirdinclined portions 134 a and 134 c, while their leading end correspondsto the sub sheet discharging tray 135. Consequently, even when africtional force is exerted by the subsequently discharged document D,the resistance force of the first and third inclined portions 134 a and134 c and sheet discharging tray 135 prevents the documents D on thesheet discharging tray 13 from moving in the sheet dischargingdirection.

The present embodiment therefore prevents the positions of the documentsstacked on the sheet discharging tray 13 from being disturbed by thesubsequently discharged document D. This improves the alignment of thedischarged documents D housed in the sheet discharging tray 13.

EFFECTS OF THE PRESENT EMBODIMENT

The sheet discharging tray 13 in accordance with the present embodimentcomprises the first to third inclined portions 134 a and 134 c, whichoffer resistance to the documents D stacked on the sheet dischargingtray 13 when they move in the sheet discharging direction. Thus, evenwhen a frictional force is exerted by the subsequently dischargeddocument D, the resistance force of the first and third inclinedportions 134 a and 134 c prevents the documents D on the sheetdischarging tray 13 from moving in the sheet discharging direction.

The third inclined portion 134 c in accordance with the presentembodiment extends both upstream and downstream in the sheet dischargingdirection by the predetermined length from the position located at thatdistance from the rear wall portion 132 of the sheet discharging tray 13which is almost equal to the vertical size of the A4-sized document D.

Thus, when A4-sized documents are stacked on the sheet discharging tray13, their leading ends contact the third inclined portion 134 c at alarge friction angle. This causes a strong resistance force to act onthe A4-sized documents on the sheet discharging tray 13. That is to say,the third inclined portion 134 c in accordance with the presentembodiment is placed so as to maximize the difficulty of moving theA4-sized documents on the sheet discharging tray 13.

The first inclined portion 134 a in accordance with the presentembodiment extends both upstream and downstream in the sheet dischargingdirection by the predetermined length from the position located at thatdistance from the rear wall portion 132 of the sheet discharging tray 13which is almost equal to half of the vertical size of the A4-sizeddocument D.

Thus, when a large number of A4-sized documents D are stacked on thesheet discharging tray 13, even if the thickness of these documents Dprecludes the leading ends of the documents D on the sheet dischargingtray 13 from coming into the third inclined portion 134 c, the firstinclined portion 134 c exerts the required resistance force on theA4-sized documents on the sheet discharging tray 13. This prevents thedocuments D on the sheet discharging tray 13 from moving in the sheetdischarging direction.

The sheet discharging tray 13 in accordance with the present inventionalso comprises the protruding portion 134 in its central portion in thewidth direction. The first and third inclined portions 134 a and 134 care provided on the top surface of the protruding portion 134.

This raises the central portion of the documents D on the sheetdischarging tray 13 in the width direction to reduce the friction areaover which the subsequently discharged document D rubs against thedocuments D on the sheet discharging tray 13.

The sheet discharging tray 13 in accordance with the present inventioncomprises the sub sheet discharging tray 135, which offers resistance toA3-sized documents D stacked on the sheet discharging tray 13 when theymove in the sheet discharging direction. Thus, even when a frictionalforce is exerted by the subsequently discharged document D, theresistance force of the first and third inclined portions 134 a and 134c and sub sheet discharging tray 135 prevents the documents D stacked onthe sheet discharging tray 13 from moving in the sheet dischargingdirection.

The sub sheet discharging tray 135 in accordance with the presentembodiment is disposed at a distance from the rear wall portion 132 ofthe sheet discharging tray 13 that is almost equal to the vertical sizeof the A3-sized document D. Thus, when A3-sized documents D are stackedon the sheet discharging tray 13, their leading ends contact the subsheet discharging tray 135 at a large friction angle. This causes astrong resistance force to act on the A3-sized documents D on the sheetdischarging tray 13. That is to say, the sub sheet discharging tray 135in accordance with the present embodiment is placed so as to maximizethe resistance against movement of the A3-sized documents D on the sheetdischarging tray 13.

In short, the present embodiment improves the alignment of thedischarged documents D on the sheet discharging tray 13 without the needfor a marked corrugation. This reduces a possible load imposed on thedocuments D. The present embodiment also eliminates the need tosignificantly incline the entire bottom wall portion 131 of the sheetdischarging tray 13. This prevents an increase in the size of thedevice. Moreover, even documents D of various sizes discharged by thesheet discharging roller 128 are not hindered from being discharged.This reliably improves the alignment of the discharged documents D onthe sheet discharging tray.

If the length of the first inclined portion 134 a in the sheetdischarging direction is set to contain the position of the leading endof B5-sized documents D stacked on the sheet discharging tray, effectssimilar to those exerted on the A4-sized documents are exerted on theB5-sized documents D.

The inclinations of the first and third inclined portions 134 a and 134c are designed so that even when the sub sheet discharging tray 135 isnot drawn out, the combination of the inclined portions 134 a and 134 cprevents A3-sized documents D stacked on the sheet discharging tray 13from moving in the sheet discharging direction. However, the drawn-outsub sheet discharging tray 135 further improves the alignment of thedischarged documents.

The protruding portion 134 in accordance with the present inventioncomprises the second inclined portion 134 b between the first and thirdinclined portions 134 a and 134 c. However, for example, as shown inFIG. 7, a bent portion 134 e may be formed between the first and thirdinclined portions 134 a and 134 c, instead of the second inclinedportion 134 b. As shown in FIG. 7, the bent portion 134 e includes ahorizontal surface, an inclined surface having a smaller gradient thanthe third surface, and an inclined surface having a gradient opposite tothat of the third surface.

The first to fourth inclined portions 134 a to 134 d in accordance withthe present embodiment are formed in the protruding portion 134 of thebottom wall portion 131. However, the present invention is not limitedto this. For example, the inclined portion may be formed all over thebottom wall portion 131. Even without the protruding portion 134,substantial effects can be produced by the first to fourth inclinedportions 134 a to 134 d formed in the bottom wall portion of the sheetdischarging tray.

In the description of the present embodiment, the sheet dischargingdevice 40 is applied to the digital copier. However, this is onlyillustrative. The present embodiment is expected to produce appropriateeffects in any application provided that the application involvesdischarging of paper.

The present invention is not limited to the above embodiments proper. Inimplementation, the components of the embodiments can be varied withoutdeparting from the spirit of the present invention. Further, variousinventions can be formed by properly combining a plurality of componentsdisclosed in the above embodiments. For example, some of the componentsshown in the embodiments may be omitted. Moreover, components of thedifferent embodiments may be appropriately combined.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A sheet discharging device comprising: a sheet discharging sectionwhich discharges sheets; and a sheet discharging tray including astacking wall portion on which discharged sheets are stacked, thestacking wall portion comprising: a first wall portion having a firstsurface which becomes higher in a direction in which sheets aredischarged; and a second wall portion connected to an upstream end ofthe first wall portion in the sheet discharging direction and having asecond surface including at least one of a horizontal surface, aninclined surface having a smaller gradient than that of the firstsurface, and an inclined surface having a gradient opposite to that ofthe first surface.
 2. The sheet discharging device according to claim 1,wherein the first surface lies within an area including a positioncorresponding to a leading end of sheets of a size substantially halfthat of the largest sheet possibly discharged by the sheet dischargingsection when the sheets are stacked on the stacking wall portion.
 3. Thesheet discharging device according to claim 1, further comprising: athird wall portion placed upstream of the second wall portion in thesheet discharging direction and having a third surface which becomeshigher in the sheet discharging direction; and a fourth wall portionconnected to an upstream end of the third wall portion in the sheetdischarging direction and having a fourth surface including at least oneof a horizontal surface, an inclined surface having a smaller gradientthan that of the third surface, and an inclined surface having agradient opposite to that of the third surface.
 4. The sheet dischargingdevice according to claim 2, further comprising: a third wall portionplaced upstream of the second wall portion in the sheet dischargingdirection and having a third surface which becomes higher in the sheetdischarging direction; and a fourth wall portion connected to anupstream end of the third wall portion in the sheet dischargingdirection and having a fourth surface including at least one of ahorizontal surface, an inclined surface having a smaller gradient thanthat of the third surface, and an inclined surface having a gradientopposite to that of the third surface.
 5. The sheet discharging deviceaccording to claim 3, wherein the third surface lies within an areaincluding a position corresponding to a central portion of sheets of asize substantially half that of the largest sheet possibly discharged bythe sheet discharging section when the sheets are stacked on thestacking wall portion.
 6. The sheet discharging device according toclaim 4, wherein the third surface lies within an area including aposition corresponding to a central portion of sheets of a sizesubstantially half that of the largest sheet possibly discharged by thesheet discharging section when the sheets are stacked on the stackingwall portion.
 7. The sheet discharging device according to claim 1,wherein the first surface has an inclination which allows a sheet beingdischarged by the sheet discharging section to slide on the firstsurface.
 8. A sheet discharging device comprising: a sheet dischargingsection which discharges sheets; and a sheet discharging tray includinga stacking wall portion on which discharged sheets are stacked, thesheet discharging tray comprising: a projecting portion having a wallportion provided in a central portion of the sheet discharging tray in awidth direction substantially orthogonal to the sheet dischargingdirection to raise a width-wise central portion of the sheets stacked onthe sheet discharging tray, the wall portion comprising: a first wallportion having a first surface which becomes higher in a direction inwhich sheets are discharged; and a second wall portion connected to anupstream end of the first wall portion in the sheet dischargingdirection and having a second surface including at least one of ahorizontal surface, an inclined surface having a smaller gradient thanthat of the first surface, and an inclined surface having a gradientopposite to that of the first surface.